tailieunhanh - Lecture Database management systems - Chapter 3: The enhanced entity - relationship (EER) model

Chapter 3: The enhanced entity - relationship (EER) model. This chapter presents the following content: EER model; Subclasses, superclasses and inheritance; specialization and generalization; constrains and characteristics; union. | Chapter 3 The Enhanced Entity - Relationship (EER) Model EER Model The basic concepts of ER modeling are not powerful enough for some complex applications. The Enhanced ER model is the extension of the original ER model with new modeling constructs. EER Model Include all modeling concepts of basic ER Additional concepts: ◦ Subclasses/superclasses ◦ Specialization/generalization, ◦ Categories, attribute inheritance Iƒt is used to model applications more completely and accurately if needed It includes some object-oriented concepts, such as inheritance Outline Subclasses, Superclasses and Inheritance Specialization and Generalization Constrains and Characteristics Union Subclasses, Superclasses In many cases an entity type has numerous subgroupings of its entities that are meaningful and need to be represented explicitly because of their significance to the database application. Ex: EMPLOYEE may be further grouped into: ◦ SECRETARY, ENGINEER, TECHNICIAN, Based on the EMPLOYEE’s Job ◦ MANAGER EMPLOYEEs who are managers ◦ SALARIED_EMPLOYEE, HOURLY_EMPLOYEE Based on the EMPLOYEE’s method of .